3.
Global Climate Change
…driving up the amount of water in
the atmosphere…
l The world is warming…
So the expectation is that future climate will be on average
both warmer and wetter
http://www.huffingtonpost.com/peter-h-gleick/the-
graph-that-should-be-_b_808747.html
Willett K.M., Jones P.D., Thorne P.W., Gillett N.P.
2010. Environ. Res. Lett. 5 025210: 1-8.

6.
Changes in rainfall seasonality
(1930-2002)
Crop seasonality is affected by both the intensity and the distribution of
the rains over time and both are affected by climate change…..
Feng et al. 2013. Nature Climate Change doi:10.1038/nclimate1907.
Mean annual rainfall
Seasonality index
Changes in the seasonality index per year

8.
Unpredictable
l Can happen, or not happen
l When it does happen, can be mild, intermediate or severe
l Can happen at different developmental stages of the plant
l Stress intensity is affected by soil composition and
weather conditions
l Stress intensity is affected by agriculture practices
Moving target
l Many different kinds of drought stress
l As many ideal phenotypes as there are kinds of drought
l Screening for drought tolerance under rain-fed conditions
is always an unreplicable experiment
Drought: A very complex, capricious
and moody customer (1)

9.
Difficult to phenotype
l Proper drought trial management is challenging
l Confounding effects of drought escape
l GxE is exacerbated in drought conditions
l Yield is a low heritability trait
l A must to include secondary traits
l Accurate trait measurement is required
Genetically very complex
l Gene effects can act in opposite directions depending on
the nature of the stress and/or the target environment
l Some gene interactions are highly dependent on the pattern
of rainfall and other environmental conditions
l Yield under drought conditions is one of the most, if not the
most, polygenic trait
Drought: A very complex, capricious
and moody customer (2)

11.
Nature’s way
l To produce at least one seed, so that the whole life cycle is
completed
l Activate adaptive mechanisms as soon as stress occurs
l Tolerance/survival generally based on a few mechanisms
Breeder’s way
l To produce as many seeds as possible
l For the crop not to sense the stress too early
l To pyramid multiple tolerance mechanisms
So to breed for DT is not only to produce more (the situation
under optimal conditions), but also to prevent the plant from
producing less
Breeding for drought tolerance is the
opposite of Nature’s approach

40.
Analysis based on an SSR (phi76) locus linked to a gene encoding catalase
(cat3), an important enzyme for maintaining cellular function under oxidative
stress conditions caused by high temperature
Changes in allelic frequency over
cycles of selection in maize
PhD thesis, Claudia Bedoya Salazar
Genetic effect must be tested in improved germplasm!

43.
Conclusion (2)
Different genetics for different crops
l Landraces and CWRs harbour novel alleles especially in crops
where allelic diversity among cultivars is limited
l Validation of adaptive alleles in elite background can be a
challenge, especially for crops with a long breeding history
l Major QTL/genes have been identified for GY components and
secondary traits in crops with:
• a short DT breeding history,
• limited allelic diversity in cultivars or
• a large LD
l Such native gene effects do not exist in a crop like maize
l The genetic effect per se of any major gene, or cluster of genes
will decrease over time with breeding effort
l Less usable in a predictive mode
l So an integrative breeding approach will be required sooner or
later

44.
Conclusion (3)
Breeding perspectives
l Breeding for grain yield under normal conditions or under high
density can be used as a substitute for DT selection
l Can be quite efficient particularly when phenotyping facilities are
limited as long as there is still a large potential for genetic gain
l In the mid- to long-term, we will need to select under drought
conditions and understand the DT mechanisms
l Linkage within clusters of DT genes must be broken
l How deeply we need to understand the mechanics of DT in order to
breed effectively for DT continues to be an open question
l Probing too deeply may be a waste of resources considering the
unpredictable nature of drought
l Breeding for drought is a numbers game aimed at pyramiding
numerous favourable alleles to enable a broad-based response to
drought conditions (timing and intensity)

46.
Vision
A future where plant breeders
have the tools to breed crops in
marginal environments with
greater efficiency and accuracy
for the benefit of the resource-
poor farmers and their families.
Mission
Using genetic diversity
and advanced plant
science to improve
crops for greater food
security in the
developing world.
The Integrated Breeding Platform (IBP), a one-stop shop providing
access to modern tools applications, and services for integrated crop
breeding with a focus on breeders in developing countries.
www.integratedbreeding.net /IntegratedBreedingPlatform /IBPlatform
• Downloadable online at:
www.generationcp.org/
drought_phenotyping
• Also available in hard copy
(limited edition).
To request a copy please
send an e-mail to:
books@generationcp.org
GCP’s phenotyping book
Drought phenotyping in crops:
from theory to practice –
available on DVD at the GCP
booth!
The CGIAR
Generation
Challenge
Programme
(GCP)
http://www.generationcp.org/